Simple Distinctions

This framework is a good starting place to understand the difference between "complicated" and "complex" systems.

Complicated systems have predictable outcomes. This predictability implies that with enough information and understanding, one can forecast the behavior of the system. If you can accurately describe what each part of the system does, you can probably predict what the entire system will do. Complicated systems are also controllable through a script or set of instructions that are designed to govern the system. 

Complex systems are inherently unpredictable. Their behavior may not be easily forecasted because they can adapt, learn, or evolve in response to changes, making their future states difficult to predict. They are not controlled by a single entity but instead are self-organizing through the interaction of their parts, like birds in a flock or the free market. The outcomes are emergent in that they arise from the interactions of the elements that would not be predicted by looking at the elements in isolation.